From the author of

From the author of

When predicting the future of any given technology, I always claim that the
easiest way of getting good results is to consider the ideal form factor for a
device. In this regard, eBooks are no different.

What, then, is the ideal form factor for an eBook reader? For the last few
hundred years, we’ve been using a device for reading that has a lot going
for it. It’s cheap to mass-produce, has a long lifespan, doesn’t
require batteries, and has a fairly simple user interface. It has some
downsides, though, the most important being size. I would estimate that around
half of my possessions by mass are books; and, while they have some aesthetic
appeal, storing them all is a nontrivial problem—one I solve by lending as
many as possible to friends who look like they need something to read.

The biggest advantage eBooks have over their traditional paper counterparts
is that eBooks are readily portable. When I was traveling a lot in 2006, I
downloaded a few dozen books from
Project Gutenberg
to my Nokia 770. This device has a lot of limitations, but the screen is
absolutely gorgeous. It’s the first device I owned that I didn’t
mind using for long periods. Although the reading experience wasn’t as
pleasant as that provided by a printed book, the fact that I could carry enough
books in my jacket pocket to last for an extended trip was a huge advantage.

How Many Pixels?

Returning to the ideal form factor question, what does an eBook reader lack
versus a printed book? In the case of the Nokia 770, the display was inferior.
But 2007 saw the commercial exploitation of a technology that has been promised
"Real Soon Now" since the mid 1990s: electronic ink. A figure of 300
dots per inch (dpi) typically is thrown around as the minimum for text to be
clear and comfortable to read. Current eInk displays provide about 166 dpi. This
is lower than the 225 dpi resolution of the Nokia 770 LCD, but more readable due
to the fact that it’s reflective rather than emissive. But even this level
of readability is still less than that of the printed page.

To keep printing costs down, most books are printed with only one color of
ink: black. A technique known as dithering gives the illusion of shades
of gray, using patterns of small black dots at a given density to simulate gray.
This technique allows printing to sacrifice some resolution in exchange for more
colors. (The dot pattern has to be smaller than the eye can discern, so the
effective resolution is lower when dithering is used.)

This technique can be applied in reverse on an electronic paper display.
Characters in text typically are stored in a vector format. A TrueType font, for
example, contains a series of Bézier paths. When a TrueType font is
printed or displayed, the curves are drawn over a regular grid of pixels. Some
of the pixels are completely covered, and these are colored black. Some are
completely uncovered, and these are colored white (that is, not printed on).
Others are partially covered. When printing, these partially covered pixels
typically are printed if they’re more than 50% covered; otherwise,
they’re not printed. Most display systems color the partially covered
pixels with a shade of gray, giving a smoother appearance than a black-and-white
image at the same resolution. Since most current electronic paper displays
support 16 shades of gray, they use this technique to increase their apparent
resolution.

The big thing missing from current electronic paper displays is true color.
Using 16 shades of gray reminds me of my first laptop, a 386 system, and is
incredibly primitive by modern standards. One big challenge for the next year
will be getting color displays into an eBook application. Three different types
of ink and the same number of levels as are currently available would give
12-bit color. This isn’t as many colors as even a cheap thin film
transistor (TFT) LCD offers, but is enough for displaying most images with only
a small loss in quality. This capability would make eBook readers convenient for
applications such as online newspapers with color photographs.

The other big limitation of current displays is that they take about 0.9
seconds to update—not bad when you consider how long it takes to turn a
page in a conventional book, but much slower than most screens, and certainly
not fast enough for video. Is video in an eBook reader interesting? Maybe. Once
you get the ability to play video, there isn’t a huge amount of difference
between an eBook reader and a portable computer. Having a dedicated device for
reading is only interesting at the moment because display technologies have
widely different sets of advantages and disadvantages. Future display
technology, whether based on organic LED, eInk, or some other system, is likely
to remove this tradeoff.